In the field of image forming apparatuses, such as a copying machine or a printer that employs an electrophotographic process or an inkjet printing system, full-color digital copying/Multi Function Printers that can reproduce color images with high image quality have been commercialized, due to advancements in digital image processing technology.
Document images duplicated by such image forming apparatuses contain text, line drawings, pictures, or combinations thereof. In order to obtain a finely reproduced image, it is necessary to perform an appropriate image process on the document.
Owing to the situation, modes, such as a text mode, a text/picture mode, or a picture mode, are prepared so as to function as operation modes of the image forming apparatuses for selecting a document type.
However, it is extremely bothersome for a user to switch between modes for each document. In addition, in many cases in which, for example, an inappropriate mode is selected, the images are significantly deteriorated, resulting in a wasted copy.
To solve the problem, there is a suggested an automatic discrimination of the document type.
For example, in Japanese Unexamined Patent Publication No. 10-126631 (published on May 15, 1998), in addition to conventional document types, such as a copy document, a silver salt film, and a halftone print, that have been subjects of classification, an image outputted by an inkjet printer is also included in the subjects of classification.
Specifically, characteristics in connection with a color reproduction area and characteristics in connection with texture are extracted from a digital color signal obtained by reading the document, and it is determined whether the document is a document outputted by an inkjet printer.
An image outputted by the inkjet printer is characterized in that brightness of cyan and magenta is greater than that of an ordinary halftone print document. This characteristic appears as a difference in the color reproduction area.
Further, because an error diffusion method or a dither method is used, there exist another characteristic where textures formed of dots exist on a white part of a paper. Although the difference in the color reproduction area between an image outputted with the inkjet printer and a document written with a highlighter is small (in a signal value read by an input apparatus, such as a color scanner, the difference in the color reproduction area between an image outputted with the inkjet printer and blue/violet lines in highlight colors is small), the image and the document can be discriminated by extracting the characteristics representative of the texture.
In Japanese Unexamined Patent Publication No. 10-126631 mentioned above, the inkjet printed image itself is recognized, and an appropriate process is carried out on the inkjet printed image, thereby improving image quality.
However, because the inkjet printer deals with various resolutions, color materials, output papers, and tone reproduction (error diffusion method, dither method), it is difficult to distinguish between all inkjet printed images. Even if the inkjet printed image is discriminated, having only one single document mode (single process) does not allow the inkjet printer to finely reproduce all inkjet printed images. For example, in a case where the document is an image outputted by an extremely high resolution inkjet printer (approximately 2800 dpi (dot per inch)) on a picture-dedicated paper, even if the document is read by an ordinary resolution input apparatus (approximately 600 dpi), it is difficult to read every single dot. Therefore, a result of reading result would be the same as that for the photographic-picture. In this case, better reproduction image is obtained by performing processing in the same manner as that for the photographic-picture.
For another example, in a case where a document is a document outputted by a low resolution inkjet printer (no more than 600 dpi) on plain paper or recycled paper, almost all dots can be read, and the color reproduction area is similar to that of a printed image. Therefore, it is difficult to determine the document as an inkjet printed image. In other words, the document has similar characteristics to that of the print document, making it difficult to be discriminated from the print document. In this case, better reproduction image is obtained by processing the document in the same manner as that for the text print document or the printed-picture document.
Further, in Japanese Unexamined Patent Publication No. 10-126631 mentioned above, in a case where an overall brightness of a document is relatively low, an inkjet printed image and a photographic-picture cannot be discriminated. Accordingly, an image cannot be finely reproduced.